This invention relates to a throttle valve controller for an internal combustion engine, having an actuator for opening/closing a throttle valve and having a fail-safe function such that, while the opening of the throttle valve is controlled with the actuator in an ordinary state, the actuator is disconnected from the throttle valve to enable a throttle valve opening control performed by operating an accelerator pedal in an abnormal state and, more particularly, to an internal combustion engine throttle valve controller suitable for motor vehicle engines.
Recently, electronic throttling type of throttle valve controllers, which now attract attention, have been provided as new throttle valve control systems for internal combustion engines mounted on vehicles, e.g., motor vehicles, to be used in place of the conventional direct throttle valve operation. In this control system, the throttle valve is controlled to be opened and closed by an actuator such as an electronic motor into which an operation amount of the accelerator pedal is fed as an electronic signal provided by a sensor after computing of the signal. Such an electronic-throttling type of throttle valve controllers have been noted. Such controllers have found applications to various kinds of engine control such as traction control effective in improving the vehicle performance, e.g., the engine power.
For electronic throttling type of throttle valve controllers, a function for ensuring a sufficient degree of safety even when an abnormality of the controller or an actuator used with the controller occurs, i.e., a fail-safe function, is indispensable.
Japanese Patent Unexamined Publication No. 2-30933 discloses a technique for achieving such a fail-safe function in such a manner that electromagnetic clutches are provided for both the connections of the throttle valve to the actuator and the accelerator pedal. The clutch on the actuator side is engaged in an ordinary state to enable an electronic control of the throttle valve with the actuator, i.e., an operation in an electronic throttling mode, and the clutch on the accelerator pedal side is alternatively engaged to enable a direct throttle valve control with the accelerator pedal in an abnormal state where an abnormality, such as a malfunction of the actuator system, has occurred. That is, an "abnormal-state auxiliary drive" mode is selected to continue driving the vehicle to a repair shop or the like in spite of the abnormality, however, the driving performance may be.
As techniques related to this kind of electronic throttling, those disclosed in U.S. Pat. Nos. 5,016,589, 5,022,369, and 5,076,231 are known. Each of these related techniques, however, was developed without considering the occurrence of a state in which the throttle valve opening provided by the actuator is controlled to be closer to the open limit than the opening to which the throttle valve is set by the accelerator pedal operation. If, in such a state, an abnormality occurs in the actuator system, the throttle valve cannot be returned to the fully-closed position when the accelerator pedal is completely released. There is raised such a problem that the performance of the fail-safe function based on these techniques is thus unsatisfactory.
In conventional techniques, if an abnormality occurs in the actuator system, the electromagnetic clutch on the actuator side is disengaged while the electromagnetic clutch on the accelerator pedal side is engaged, thereby forming an "abnormal-state auxiliary drive" mechanism. At this time, however, if the throttling system is in a state such as that described above, the throttle valve having an opening greater than the opening corresponding to the accelerator pedal operation position is directly connected to the accelerator pedal, and the throttle valve cannot be fully closed by releasing the accelerator pedal. That is, there is a possibility of a serious accident, i.e., self-speeding of the vehicle. Thus, a complete fail-safe function has not been achieved.
Moreover, the above-described conventional techniques were developed without sufficiently considering cost reduction means. They require two clutches and therefore entail the problem of a high manufacturing cost.
An object of the present invention is to provide an internal combustion engine throttle valve controller having a construction advantageous in terms of cost and enabling, by a fail-safe function, "abnormal-state auxiliary driving" performed by the accelerator pedal operation in a case where an abnormality such as a failure has occurred in the actuator driving system, whereby the risk of occurrence of a serious accident such as self-speeding of the vehicle can be eliminated substantially completely.
To achieve this object, one of a flexing driving force transmission mechanism and a fluid driving force transmission mechanism is provided at a driving force connection between a member displaced with the operation of an accelerator pedal and an opening/closing drive member of a throttle valve to absorb the difference between the opening of the throttle valve controlled with the actuator and the opening to which the throttle valve is to be set by the accelerator pedal operation.
Each of the flexing driving force transmission mechanism and a fluid driving force transmission mechanism serves to cancel out the influence of the operated position of the accelerator pedal by absorbing a movement of the throttle valve caused by the actuator and to enable the throttle valve to be opened/closed through the accelerator pedal while equalizing the throttle valve opening to the opening set by the accelerator pedal, when the actuator is disconnected from the throttle valve by the driving force connection/ disconnection means.
In a case where an abnormality such as failure has occurred in the actuator driving system, the throttle valve operation by the accelerator pedal is enabled to provide for an "abnormal-state auxiliary drive" function, while the throttle valve is returned to the accelerator pedal operated position by balancing of springs constituting the flexing driving force transmission mechanism or by the fluid driving force transmission mechanism. It is thereby possible to prevent occurrence of a serious accident such as self-speeding of the vehicle during "abnormal-state auxiliary driving" and to achieve a complete fail-safe function and improved reliability of the control system.
Only one electromagnetic clutch will suffice to constitute the driving force connection/disconnection apparatus. Therefore the arrangement of the present invention is also advantageous in terms of cost.